The effect of calcination and sintering temperature on microstructural and electrical properties of YBa2Cu3O7−x

The effect of calcination and sintering temperature on microstructural and electrical properties of YBa2Cu3O7−x

Abstracts accommodate up tp 1.7 lithium atoms per unit formula at an average potential of 2 volts resulting in a theoretical energy density of of 530...

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Abstracts

accommodate up tp 1.7 lithium atoms per unit formula at an average potential of 2 volts resulting in a theoretical energy density of of 530 W h / k g compared to 480 for TiS2 cathodes. The ability of this n e w layered oxide to intercalate water molecules will a~so be presented. The F.Hect of Calcination and Sinterln 8 Temperature on Microstrudural a~td L'le,.-i,ical Properties of YBazCu3OT.x i. A. T. Taylor, David l ~ : k e ~ and Prinya 5ainamthip, NYS College of Ceramics, USA.

Processing bulk superconductors in the Ba-Y-Cu-O system is complicated by the multiphase equilibria demonstrated by the oxides of yttrium, copper and barium between 800 ° ~r~d 1100°C. Calcination of barium carbonate, yttria and cupric oxide at 975°(= for 24 hours produces phase pure Ba-Y-Cu-OT-x. Compacts prepared from this calcined powder sintered in the presence of oxygen to 950-1050 do not necessarily demonstrate superconductivity; neither zero resistivity nor Meissner effect. The same raw material calcined a.t 850 °C for 24 hours results in a multiphase powd,er containing Ba-Y-Cu-OT.x, barium cuprate and BaY2CuOs. Compacts sintered frcm this powder sintered to more than 1000°C demonstrate zero r~sistivity and a significant Meissner effe~;t. Details of this study describing the phases and electrical properties resulting from different firing schedules will be presented. Solid Stzte Photoreactivity of Metal Complexes of Substltv.ted Cyclopentanones Chari~ R. T b e o c h a r i s , Adrian C. Perryman, Maxw.~ll Muir, Alison M. Clark, and Manuel J. Godden, Brunel University, U.K. The benzylidene cyclopentanone framework can be converted into a ligand for metal ions, either by irtroducing hydroxyl substituents on the phenyl rings, or a malonic group at the 3- position of the five member ring. Changes in packing and hence reactivity, can be achieved by changing the coordinated ~ansition metal ,.a,v,,.-"^- .r~.^,,,~,~,,~:-~'",,,d . . . . transformations encoun'ered, were I 2+2 I cycloaddition, decarboxylation and dehydration. Carbon dioxide evolved during decarboxylation gave rise to a single narrow peak in the FTIR spectrum, indicating that these remained trapped within the reacting crystallites.

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Influence of the Catalyst on the Structure and Conductivity of a New (CH)x A. G. MacDiarmid and G. C. Farrington, University of Pennsylvania, USA. Different new catalysts based on transition metal campounds of groups Iv'b, Vb, VIb and VIIlb combined with a reducing agent such as: triethylaluminum and n-butyllithium in various solvents; toluene and silicone oil, were used for the polymerization of acetylene. By changing the catalyst, cocatalyst, solvent and polymerization conditions, a large variety of polyacetylenes were obtained. The polyacetylenes were characterized by SEM, FTIR and C l~ NMR spectroscopies. Some of the new polymers were stretched mechanically and then doped electrochemically or chemically by various doping agents. Thus highly conducting thick (20 Ixm) and transparent films (0.11~m) were obtained, ,with conductivities of 104 S / c m and improved properties. After modification of the standard catalyst system (Ti(OBu)4-AIEt3-silicone oil) by the introduction of some additional reducing agents, conductivities as high as 105 S/cm, after elongation and doping of the polymers, were reached. h,fluence of the Precipitation Method on the Microstructure and Sinterability of Yttria C. Tool and E. H. P. Cordfunke, Netherlands Energy Research Foundation, The Netherlands. 3interable yttrium oxide powder can be prepared by precipitating yt~R1m hydroxide (or carbonate) with ammonia. The influence of the treatment of the powder after precipitation (washing and calcination) is k n o w n from the literature, but little is known about the parameters during precipitation. The influence of some parameters of the precipitation reaction on the microstructure and sinterability of the powder (such as yttrium (HI) starting concentration, acidity, hydroxide concentration and rate of adding the precipitant solution) was investigated. The microstructure of sintered compacts was investigated by SEM. Below 1675 K the grain size of all compacts is below 0.41~nl. Above this temperature the grain growth depends on the parameters during predpitaff,on; at 18,~5 K a,~ ~ . ; ~ s~e varied between 1.2 and 9 .urn.